Small protests broke out in both cities, but authorities say security measures for the pope — who angered Muslims worldwide with comments in September on Islam and violence — will be tighter than they were for the visit of U.S. President George W. Bush.
Benedict is to arrive at the Ankara airport on Tuesday at around noon, where he will meet briefly with Turkish Prime Minister Recep Tayyip Erdogan, who waited until the day before Benedict's arrival to announce that he would make time to meet the pope.
News reports say some 3,000 police officers have been assigned to guard the pope upon his arrival in the dusty, sprawling capital Ankara. Snipers will watch from hillsides and tall buildings, and armored vehicles and riot police will be stationed near the areas he is scheduled to visit.
Police also were mobilizing and staking out spots in Istanbul, where Benedict will spend most of his four days in Turkey.
"We have taken all the necessary measures and observations of the route the pope [will travel] and the places the pope will visit," Istanbul police spokesman Ismail Caliskan said.
On Monday, a group of around 100 pro-Islamic demonstrators displayed what they said were a million signatures for a petition demanding that the Haghia Sophia, now a museum in Istanbul, be declared a mosque and opened to worship for Muslims.
The Haghia Sophia was built in the 6th century as a Christian church, but was converted to a mosque in 1453 when Islamic armies conquered the city — then a Christian metropolis called Constantinople.
In a speech on Sunday, Benedict said he was coming to Turkey as a friend of the Turks and asked his followers to pray for him. That same day, more than 25,000 Turks showed up to a mass anti- Vatican protest in Istanbul, asking the pope to stay at home.
The visit to Turkey will be a test of whether this pope can soften some of the Christian-Muslim tensions that boiled over after Benedict quoted a Byzantine emperor who characterized some of the teachings of Islam's prophet Muhammad as "evil and inhuman."
The visit will also be a test of the Turkish public's willingness to tolerate criticism of Islam and their ability to coordinate a massive and potentially problematic visit.
After spending Tuesday night in Ankara, Benedict will visit Ephesus and Istanbul, where he will meet with Bartholomew I, the Istanbul-based leader of the world's 300 million Orthodox Christians.